Data from several studies in men demonstrate that cardiorespiratory fitness is associated with lower cardiovascular disease (CVD) mortality. However, data on this relationship are limited in women and only available for patients evaluated at a fitness-oriented medical clinic, raising questions about the generalizability of results. Thus, it is important to determine whether the relationship between fitness and lower CVD mortality exists in a more representative sample of women and is comparable for women and men within the same study sample. There is preliminary evidence in men that even moderate levels of cardiorespiratory fitness may significantly attenuate the relationship found between the degree of adiposity, usually measured by body mass index (BMI), and higher CVD mortality. However, in most observational studies that have related BMI to mortality, neither level of physical activity or fitness has been included in the analyses. Given the difficulty that many overweight adults experience when losing weight, it is extremely important to determine whether being more physically fit would negate some or much of the increased risk for CVD associated with being overweight or obese. To date, this interaction between adiposity and cardiorespiratory fitness has not been examined in women or in representative samples of US men. The Lipid Research Clinics (LRC) Mortality Follow-up Study (1972-1995) consists of a large national sample of 4121 women and 4704 men 30 years and older with 23 years of mortality follow-up. We will use these data to examine two specific aims in women and men: (1) whether cardiorespiratory fitness is associated with subsequent CVD mortality, and (2) whether fitness attenuates the risk of CVD mortality associated with obesity. To date, no research team has analyzed the LRC 23-year follow-up data. The strengths of the LRC data include a national sample recruited from 10 US population centers, sufficient numbers of deaths for women (n=349) and men (n=532), substantial years of follow-up, and well-characterized measures of CVD risk factors including cardiorespiratory fitness measured by an exercise treadmill test.